Ziegler-Natta (Z-N) catalyst systems can be used to produce linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE) resins having excellent solid state properties. However, the Z-N-catalyzed polymers have shown limited usefulness for wire-and-cable applications because the polymers can have poor extrusion performance.
On the other hand, chromium-catalyzed LLDPE, MDPE, and HDPE have proved useful in wire-and-cable applications. Those products have demonstrated both excellent extrusion capability and retention of acceptable solid state properties. However, the chromium-catalyzed products show slower reactor production rates than the Z-N-catalyzed counterparts, adversely affecting the cost of making these polymers.
Because Z-N catalyzed polymers have production cost advantages over chromium-catalyzed polymers, it is desirable to produce Z-N catalyzed polymers that retain their excellent solid state properties while demonstrating extrusion capability similar to that of chromium-catalyzed polymers. It is further desirable that the Z-N catalyzed polymers provide extrudate surfaces, melt strength, toughness, environmental stress crack resistance, and heat deformation similar to or better than those properties of chromium-catalyzed polymers.